This invention relates generally to computed tomography (CT) imaging systems and more particularly to methods and apparatus for increased quality imaging, especially of moving objects, in distributed x-ray source CT imaging systems.
In computed tomography (CT) imaging systems employing rotating gantries, fan beam projections are collected linearly (progressively) at a regular sampling interval in an angular direction. For cardiac imaging, heart motion produces motion artifacts, the severity of which depend upon the speed of a rotating gantry incorporating an x-ray source and detector array. Projection data must be collected rapidly to avoid these motion artifacts. This requirement on the collection of projection data imposes technically challenging requirements on the speed at which the gantry must be able to rotate and on the flux output of the x-ray tube used as the x-ray source.
In at least one known rotating gantry CT imaging system, projection data for the same cardiac phase acquired during multiple heart cycles is used to reduce motion artifacts. An electrocardiogram (EKG) signal is acquired concurrently during a scan, or a pseudo-EKG signal is generated using the projection data itself to aid in retrospective identification of projection data acquired at a particular phase of the cardiac cycle. Because heart motion is assumed to be regular and periodic in this artifact reduction method, any irregularity or aperiodicity of heart motion will result in a degradation in image quality.
Another known CT imaging system utilizes an electrically steered electron beam to generate a moving x-ray beam. This imaging system can effectively suppress motion artifacts, but the motion-suppressed images have a relatively low signal-to-noise ratio.